A circuit arrangement of the type referred to above is known for the area of motor vehicle engineering from the German patent publication DE-A1-38 41 610.
In combustion-engine machines, electrical energy is required, for the operation of controls which typically is made available from batteries or is generated by generators driven by the engine. The employment of batteries, especially in portable machines, entails an additional expense, particularly as the long-term storage volume is limited. Moreover, in the batteryless operation as is provided in the DE-A1-38 41 610 publication for a motor vehicle, the voltage generated by the normal generator through the starting process does not provide sufficient energy for operating additional controls. However, this will be necessary in the future when engines with injection valves are more commonly used in order to actuate a valve or the like.
The applicants have designed a power supply for an electrically-controlled chain saw which dispenses additional energy. In this case, however, it did prove disadvantageous that a part of the ignition energy was used for the starting process so that, on account of the power withdrawal connected herewith, the starting behavior deteriorated. Since, in the case of portable machines, the starting behavior significantly affects operating comfort, such a solution is not devoid of problems.
Thus, an objective of the invention is to provide a circuit arrangement which permits a reliable power supply, without the employment of booster batteries, which can deliver power in the starting phase with the requisite rated d.c. voltage and which, at the same time, is simple and sturdy in its construction.